Abstract 244: Inhibition of atypical PKC signaling enhances the sensitivity of glioblastoma cells towards Temozolomide therapy

Abstract

Abstract Glioblastoma is a highly aggressive brain cancer which has a mean survival rate of only 12 months. Current treatment options of glioblastoma include chemotherapy and limited surgical resection. Temozolomide (TMZ) is the current therapeutic choice for chemotherapy but has severe limitations due to development of resistance that occurs by genetic modification and constitutive activation of several other pathways. Therefore, to overcome Temozolomide resistance and to prevent recurrence of the disease a more effective therapeutic approach is required. One of the signaling pathways that contribute to the aggressive behavior of glioma cells is the activation of PKC signaling. Of the various PKC isoforms, the atypical PKCs, PKC ζ and ι were found to be over-expressed in glioblastoma tissue samples compared with normal brain tissue and high atypical PKC levels were correlated with increased cellular proliferation and invasiveness of glioma cells. [4-(5-amino-4-carbamoylimidazol-1-yl)-2, 3-dihydroxycyclopentyl] methyl dihydrogen phosphate also known as ICA-1 was used as a specific inhibitor of PKC-ι and [8-hydroxynaphthalene-1,3,6-trisulfonic acid] also known as ζ-Stat was used as a specific inhibitor of PKC- ζ. T98G and U87 glioblastoma cells were treated with ICA-1 monotherapy (7.5µM), ζ-stat monotherapy (10 µM), TMZ monotherapy at varying doses, TMZ combined with ICA-1 (7.5µM) and TMZ combined with ζ-stat (10 µM) for five consecutive days and analyzed for cell viability by WST assay. Results exhibited that ICA (7.5µM) when combined with TMZ showed significantly increased cytotoxicity compared to TMZ monotherapy. Annexin-V/PI assay revealed that combination treatment with TMZ and ICA nucleotide (7.5µM) significantly increased the number of dead cells and the number of cells undergoing late apoptosis when compared to TMZ monotherapy. This study offers the first evidence for the novel combination of ICA-1 with TMZ to induce robust apoptosis in a Caspase-3 mediated mechanism. Scratch assay results also showed that inhibition of PKC-ζ by ζ-Stat lead to decreased invasion compared to control. Our studies suggest that atypical PKCs particularly PKC-ι might be an important therapeutic target in the treatment of glioblastoma. Citation Format: Avijit Dey, Rekha Patel, Tracess Smalley, Wishrawana Sarathi Ratnayake, Anisul Islam, Mildred Acevedo-Duncan. Inhibition of atypical PKC signaling enhances the sensitivity of glioblastoma cells towards Temozolomide therapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 244.